How to make it

For the Cake:

Preheat oven to 350° F. Butter two 9-inch square or round cake pans with 2-inch-high sides. Line bottoms with waxed paper. Butter and flour waxed paper. Bring 3/4 cup water to simmer in saucepan. Place cocoa in small bowl. Gradually whisk in hot water. Whisk in buttermilk and extract. Mix flour and baking soda in medium bowl. Using electric mixer, beat butter in large bowl until fluffy. Gradually add sugar, beating until light. Add eggs 1 at a time, beating well after each addition. Add dry ingredients alternately with cocoa-buttermilk mixture in 2 batches each, beating just until combined.

Divide batter between prepared cake pans. Sprinkle with chocolate chips. Bake until tester inserted into center of each cake comes out with some moist crumbs attached, about 20 minutes. Cool cakes in pans on racks 15 minutes. Run small sharp knife around pan sides to loosen cakes. Turn out cakes onto foil-lined racks. Carefully peel paper from cakes and cool completely. (Can be prepared 1 day ahead. Cover tightly and refrigerate.)

For the Frosting:

Bring whipping cream and corn syrup to simmer in heavy large saucepan. Reduce heat to low. Add chocolate; whisk until smooth and melted. Stir in peppermint extract. Refrigerate until mixture just thickens to spreading consistency, stirring frequently, about 2 hours.

Place 1 cake layer on platter. Spread 2 cups frosting over. Top with second cake layer. Using icing spatula, spread remaining frosting in thick decorative swirls over top and sides of cake. (Can be prepared 8 hours ahead; cover with cake dome and let stand at room temperature.) Garnish cake with mint sprigs.